Requirements and availability of prey for northeastern pacific southern resident killer whales

Couture, Fanny; Oldford, Greig; Christensen, Villy; Barrett‐Lennard, Lance G.; Walters, Carl J.

doi:10.1371/journal.pone.0270523

Cited by 8 publications

(8 citation statements)

References 38 publications

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“…Here, we used an IPM approach that jointly estimates the effect of Chinook salmon abundance on SRKW survival and fecundity rates. Declining abundances in some populations of Chinook salmon, SRKWs' preferred prey resource, are potentially linked to their low population growth rates, and a failure to recover from a period when dozens of animals were removed from the population (Couture et al 2022;Wade et al 2012;Wasser et al 2017;Williams et al 2011). However, uncertainty has remained as to precisely how low prey availability may translate to limited population growth, and conventional statistical modeling approaches are not well-suited for addressing the problem.…”

Section: Discussionmentioning

confidence: 99%

“…Diet information from SRKWs suggests a heavy reliance on Chinook salmon (Ford et al 2016); populations of both hatchery‐ and wild‐origin salmon have experienced fluctuations in both survival and abundance since the 1970s (Freshwater et al 2022; Ruff et al 2017). Furthermore, the abundance of large Chinook salmon of older age classes has also declined in populations along the West Coast of North America over the last four decades (Couture et al 2022; Ohlberger et al 2018). Abundance of Chinook salmon is thought to be associated with killer whale demographic rates and has been the primary focus of recovery efforts (Ward et al 2009).…”

Section: Introductionmentioning

confidence: 99%

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Identifying drivers of demographic rates in an at‐risk population of marine mammals using integrated population models

Nelson,

Ward,

Linden

et al. 2024

Ecosphere

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Effective conservation of threatened populations requires identification of the processes limiting recovery. When multiple population processes are potentially limiting, they are sometimes analyzed independently, often using different datasets. Analytically, this is suboptimal, as processes are often correlated, which can lead to biased estimates of parameters and quantities of interest. Integrated population models (IPMs) can synthesize several data streams in the same probabilistic framework to circumvent these issues. Lack of prey was identified as one of the primary threats to recovery of critically endangered southern resident killer whales (SRKWs), Orcinus orca. Previous studies have correlated SRKW demographic rates with indices of Chinook salmon Oncorhynchus tshawytscha abundance, but these approaches have modeled reproduction and survival independently. We developed an IPM for SRKWs that models both processes simultaneously, as a function of Chinook salmon abundance along the west coast of North America. We used this model to evaluate the relationship between Chinook salmon abundance and demographic rates of SRKWs, with the goal of updating our understanding of a potential causal relationship between prey availability and SRKW population dynamics, and how these relationships may have changed over time. Results suggest that SRKW mortality rates are more strongly associated with Chinook salmon abundance than birth rates. Our analysis also suggests northern resident killer whale abundance could also be affecting SRKW carrying capacity, possibly through competition over shared prey resources. The IPM fit observed total abundance data well and predicted temporal changes in population demographics with reasonable accuracy, but small sample size may have opacified model selection. Our approach offers a valuable tool for predicting the response of the SRKW population to alternative management strategies involving the recovery of Chinook salmon stocks in the eastern Pacific.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Identifying drivers of demographic rates in an at‐risk population of marine mammals using integrated population models

Nelson,

Ward,

Linden

et al. 2024

Ecosphere

View full text Add to dashboard Cite

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“…The intensifying predation by those marine mammals on mature fish can affect the average body size, maturation timing, and life-history characteristics of the Chinook salmon populations through the selective removal of larger fish [ 99 ]. In addition, leaving smaller Chinook salmon implies a reduction in caloric value, which could further affect other marine mammals feeding on similar preys, including SRKW [ 100 , 101 ]. Although one could argue that SRKW might have access to larger fish the same way NRKW do, recent evidence suggests that SRKW might exhibit different foraging strategies than NRWK [ 102 ].…”

Section: Discussionmentioning

confidence: 99%

The combined effects of predation, fishing, and ocean productivity on salmon species targeted by marine mammals in the northeast Pacific

Couture,

Christensen,

Walters

2024

PLoS ONE

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Along the northeast Pacific coast, the salmon-eating southern resident killer whale population (SRKW, Orcinus orca) have been at very low levels since the 1970s. Previous research have suggested that reduction in food availability, especially of Chinook salmon (Oncorhynchus tshawytscha), could be the main limiting factor for the SRKW population. Using the ecosystem modelling platform Ecopath with Ecosim (EwE), this study evaluated if the decline of the Pacific salmon populations between 1979 and 2020 may have been impacted by a combination of factors, including marine mammal predation, fishing activities, and climatic patterns. We found that the total mortality of most Chinook salmon populations has been relatively stable for all mature returning fish despite strong reduction in fishing mortality since the 1990s. This mortality pattern was mainly driven by pinnipeds, with increases in predation between 1979 and 2020 mortality ranging by factors of 1.8 to 8.5 across the different Chinook salmon population groups. The predation mortality on fall-run Chinook salmon smolts originating from the Salish Sea increased 4.6 times from 1979 to 2020, whereas the predation mortality on coho salmon (Oncorhynchus kisutch) smolts increased by a factor of 7.3. The model also revealed that the north Pacific gyre oscillation (NPGO) was the most important large-scale climatic index affecting the stock productivity of Chinook salmon populations from California to northern British Columbia. Overall, the model provided evidence that multiple factors may have affected Chinook salmon populations between 1979 and 2020, and suggested that predation mortality by marine mammals could be an important driver of salmon population declines during that time.

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“…A recent assessment of April-October Chinook salmon availability for the SRKW in the Salish Sea and off the west coast of Vancouver Island over the last 40 years found that overall salmon abundance available to the whales has declined, with the models predicting an energetic deficit for the whales in six years across the study period, including 2018, 2019, and 2020, the final year for which analysis occurred ( Couture et al, 2022 ). The relative contribution of different Chinook salmon stocks and their availability to SRKW has been changing, with Columbia River stocks specifically increasing in their importance to SRKWs compared to Puget Sound stocks.…”

Section: Discussionmentioning

confidence: 99%

2018–2022 Southern Resident killer whale presence in the Salish Sea: continued shifts in habitat usage

Shields¹

2023

PeerJ

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The fish-eating Southern Resident killer whales (Orcinus orca) of the northeastern Pacific are listed as Endangered in both the USA and Canada. The inland waters of Washington State and British Columbia, a region known as the Salish Sea, are designated as Southern Resident critical habitat by both countries. The whales have historically had regular monthly presence in the Salish Sea, with peak abundance occurring from May through September. In recent years, at least partially in response to shifting prey abundance, habitat usage by the Southern Residents has changed. As conservation measures aim to provide the best possible protection for the whales in their hopeful recovery, it is key that policies are based both on historic trends and current data. To this aim, our study shares 2018–2022 daily occurrence data to build upon and compare to previously published whale presence numbers and to demonstrate more recent habitat shifts. Based on reports from an extensive network of community scientists as well as online streaming hydrophones, every Southern Resident occurrence was confirmed either visually or acoustically. Documented here are the first-ever total absence of the Southern Residents in the Salish Sea in the months of May, June, and August, as well as their continued overall declining presence in the spring and summer, while fall and winter presence remains relatively high. It is key that management efforts consider these shifting presence patterns when setting both seasonal and regional protection measures aimed at supporting population recovery.

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Requirements and availability of prey for northeastern pacific southern resident killer whales

Cited by 8 publications

References 38 publications

Identifying drivers of demographic rates in an at‐risk population of marine mammals using integrated population models

Identifying drivers of demographic rates in an at‐risk population of marine mammals using integrated population models

The combined effects of predation, fishing, and ocean productivity on salmon species targeted by marine mammals in the northeast Pacific

2018–2022 Southern Resident killer whale presence in the Salish Sea: continued shifts in habitat usage

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